Process of producing polyethylene terephthalate



United States Patent 3,406,153 PROCESS OF PRODUCING POLYETHYLENE TEREPHTHALATE Edwin E. Eaton, Circleville, Ohio, and James R. Small, Mount Vernon, Ind., assignors to E. I. du Pont. de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Continuation-impart of application Ser. No. 274,903, Apr. 23, 1963, which is a continuation-in-part of application Ser. No. 195,325, May 16, 1962. This application Aug. 9, 1966, Ser. No. 571,179

4 Claims. (Cl. 260-75) ABSTRACT OF THE DISCLOSURE In the manufacture of highly polymeric linear polyesters of aromatic dicarboxylic acids, e.g., polyethylene terephthalate, the polymerization reaction is carried out in the presence of from 0.05% to 1% by weight, based on the weight of alkyl ester of the aromatic dicarboxylic acid employed, of an organic phosphonate selected from the group consisting of hydroxy-polyoxyethylene hydroxymethyl phosphonate, hydroxy polyoxyethylene chloromethyl phosphonate, hydroxy-polyoxyethylene trichloromethyl phosphonate, bis[2-brornoethyl(phenyl)] ethylene diphosphonate, bis(2-bromoethyl)phosphonate, bis(2-chloroethyl)phosphonate, the reaction product of triethyl phosphite and 2-chloroethanol, the reaction product of triethyl phosphite and 2-bromoethanol, and the reaction product of dimethyl methylphosphonate and ethylene glycol. The resulting products have the advantageous properties, particularly with respect to film made therefrom, normally associated with the presence of phosphorus compounds in the polyester composition, and the disadvantages generally incident to reaction of the phosphorus compound with catalysts commonly employed in the manufacture of the polyesters are avoided.

This application is a continuation-in-part of our now abandoned application Ser. No. 274,903, filed Apr. 23, 1963, which in turn is a continuation-in-part of our now abandoned application Ser. No. 195,325 filed May 16, 1962.

The production of the novel class of fil'mand fiberfor-rning polyesters of terephthalic acid and a glycol of the series HO(CH ),,OH where n is an integer from 2-10, inclusive, is fully disclosed in US. Patent 2,465,319 to Whinfield and Dickson. From a commercial standpoint, one of the most attractive polymers of this class is polyethylene terephthalate prepared by carrying out an ester interchange between ethylene glycol and dimethyl terephthalate to form bis-2-hydroxy ethyl terephthalate monomer which is polymerized to polyethylene terephthalate under reduced pressure and at elevated temperatures, and in the presence of suitable catalysts.

In the manufacture of polyethylene terephthalate film from a polymer prepared in accordance with the general teaching of aforementioned US. Patent 2,465,319 it is preferred to carry out in a continuous operation the steps of (1) ester interchange between glycol and dimethyl terephthalate in the presence of an ester-interchange catalyst to form bis-Z-hydroxyethyl terephthalate monomer; (2) polymerization of the monomer in the presence of a polymerization catalyst to form a high molecular weight polyethylene terephthalate; (3) melt-extrusion of the polymer into film. The operation of such a continuous process, however, is fraught with several serious difficulties. One of the most formidable difficulties encountered in this process, for example, is the formation of striations in the film. These striations seem to originate at the lips of the extrusion die from which the polymer is formed into film. The appearance of striations necessitates closing down the operation for cleaning the lips of the die. During these interruptions the polymer must be dumped resulting not only in a loss of production time but loss of material as well. Another serious difficulty is undesirable color-formation (i.e., yellowing) which appears to take place during the polymerization stage and is apparently ascri-bable to the polymerization catalysts. It has been found that the first of these difficulties is obviated by the addition to the reaction mixture preferably in the polymerization stage, of a small amount of a mmonium phosphate or phosphite. The presence of such phosphorous material in the polymer also serves to greatly enhance the insulation resistance of the polymeric film and hence increases its value and application as a dielectric material. The addition of these phosphorus compounds, while greatly improving the insulation resistance of the film, inhibiting color-formation, and materially eliminating film striations and thereby reducing lost production time for extrusion die cleaning, has two serious drawbacks. It is commonly known that monoammonium phosphate, for example reacts with many of the catalysts, commonly employed, to form solid precipitates. This condition results in the problems of (1) more rapid plugging of the polymer filtration system and, presumably because of the conversion of the catalyst to inactive forms, (2) lower polymerization activity which limits polymer production.

These problems also arise with respect to other linear polyesters. Thus, although the invention will be described primarily as it applies to linear polymeric esters of terephthalic acid, it should be understood that the invention is also applicable to linear polymeric esters of aromatic dicarboxylic acids, in general.

It is an object of this invention, therefore, to provide an improved process of preparing linear polymeric esters and, particularly, highly polymeric linear terephthalate esters. Another object is to provide for the continuous production of shaped structures (e.g., film) therefrom which substantially avoids the aforementioned maintenance and catalyst reaction problems. A further object is to prepare polyethylene terephthalate film having enhanced insulation resistance which is particularly useful as a dielectric in capacitors, etc. A still further object is to provide polymeric esters of aromatic dicarboxylic acids and particularly polyethylene terephthalate which are substantially free of undesirable coloration. The fore-. going and additional objects will be apparent from the detailed description which follows.

These objects are realized by the present invention which briefly stated, comprises in a process of making highly polymeric polyethylene terephthalate wherein an initial reaction charge selected from the group of reactants comprising (A) an alkyl ester of terephthalic acid having 1-7 carbon atoms in the alkyl group and a polymethylene glycol having from 2l0 carbon atoms and (B) bis-Z-hydroxyalkyl terephthalate and low molecular weight polymers thereof having an intrinsic viscosity not greater than 0.2 is reacted in the presence of a catalyst system effective to promote (1) ester interchange and polymerization in the case of (A) and (2) polymerization in the case of (B); the improvement which cornprises carrying out the polymerization until a film-forming polymer is produced in the presence of from 0.05% to 1% by weight, based on the weight of alkyl ester of terephthalic acid in the initial reaction charge, of an organic phosphonate selected from the group consisting of hydroxy-polyoxyethylene hydroxymethyl phosphonate, hydroxypolyoxyethylene chloromethyl phosphonate, hydroxy-polyoxyethylene trichloromethyl phosphonate, bis [2-bromoethyl(phenyl)]ethylene diphosphonate, bis(2- bromoethyl phosphonate, bis 2-chl0roethyl phosphonate, the reaction product of triethyl phosphite and 2-chloroethanol, the reaction product of triethyl phosphite and 2- bromoethanol, and the reaction product of dimethyl methylphosphonate and ethylene glycol.

The invention is also applicable to a process wherein the initial reaction charge is selected from the group of reactants comprising (A) an alkyl ester of an aromatic dicarboxylic acid having 1-7 carbon atoms in the alkyl group and a polymethylene glycol having from 2-10 carbon atoms and (B) bis-hydroxyalkyl ester of an aromatic dicarboxylic acid and low molecular polymers thereof having an intrinsic viscosity not greater than 02; and the charge is reacted in the presence of a catalyst system effective to promote ester interchange and polymerization in the case of charge (A) and polymerization alone in the case of charge (B). Some of the more important aromatic dicarboxylic acids include COOH COOH wherein R is selected from the group consisting of an alkylene chain having 1-3 carbon atoms,

the preferred ones being terephthalic acid; isophthalic acid, bibenzoic acid; 1,5-na-phthalene dicarboxylic acid; 2,6-naphthalene dicarboxylic acid; and 2,7-naphthalene dicarboxylic acid. The preferred polymethylene glycol is ethylene glycol. However, one or more (at least one) of the following may be used: ethylene glycol, diethylene glycol, propylene glycol, butylene glycol, decamethylene glycol, neopentyl glycol and trans-bis-1,4-(hydroxymethyl)cyclohexane.

The organic phosphonate may be added to the reaction mixture at any time prior to, or during polymerization, and should be present in the reaction mixture in an amount within the range of from 0.05% to 1% by weight based on the weight of the alkyl ester of the aromatic dicarboxylic acid (the dimethyl terephthalate) in the initial reaction charge. When less than 0.05 of phosphonate is used the beneficial results of our invention are not realized. On the other hand, if more than 1% of phosphonate is added to the reaction mixture, the rate of polymerization decreases, the melt viscosity of the polymer increases with respect to the intrinsic viscosity, and an undesirable gray cast is imparted to film cast from the polymer.

and

Typical catalyst systems utilized for the ester interchange between the alkyl ester of an aromatic dicarboxylic acid having 1-7 carbon atoms, preferably dimethyl terephthalate and a polymethylene glycol having 2-10 carbon atoms, preferably ethylene glycol, and the subsequent polymerization to the polyester, preferably polyethylene terephthalate, and which are compatible with the organic phosphonate additives of this invention, are listed in the following table:

TABLE I Percent composition range System: (based on weight of DMT) 1 Zinc acetate dihydrate 0.01-005 Lithium hydride 0003-0015 Antimony trioxide 002-004 Manganous acetate 00001-0003 Antimony trioxide 000005-0003 Zinc acetate dihydrate 0.01-005 Antimony trioxide 0.02-0.04 Zinc acetate dihydrate 0.01-0.10 Tetraisopropyl titanate 00015-00045 Zinc acetate dihydrate 0.02-005 Tetraisopropyl titanate 00015-00045 Zinc acetate dihydrate 0.02-005 Lithium hydride 0.003-0015 Lanthanum titanate 001-010 Lanthanum oxide 0.01-010 Lanthanum titanate 0.01-010 Cerium oxide 0001-005 Lithium hydride 0.003-0015 Zinc acetate dihydrate 001-005 Cobaltous acetate 0.01-005 Lithium hydride 0003-0015 Cadmium acetate 0.01-015 Cobaltous acetate 0.01-015 Antimony trioxide 0.01-010 Zinc acetate dihydrate 0.02-0.05 Antimony trioxide 002-005 Magnesium acetate dihydrate 0003-001 Litharge (PbO) 0005-01 Antimony trioxide 001-015 Cobaltous acetate 001-015 Litharge 0.01-010 Cobaltous acetate 0.01-015 Litharge 001-010 Antimony trioxide 001-010 Calcium acetate 0.01-015 Antimony trioxide 001-010 Litharge 0.005-1.0 Manganous formate 0.1-0.10 Silico Tungstic acid 0.01-010 1 Dimethyl terephthalate.

Representative catalyst systems, compatible with phosphonate additives, utilized for polymerization of the bishydroxyalkyl ester of an aromatic dicarboxylic acid, preferably bis-Z-hydroxyethyl terephthalate are listed in the following table:

TABLE II Percent composition In the preferred embodiment of this invention polyethylene terephthalate film is produced continuously in a series of sequential continuous steps comprising reacting dimethyl terephthalate with ethylene glycol under esterinterchange conditions in the presence of an ester-interchange catalyst to form bis-Z-hydroxyethyl terephthalate having an intrinsic viscosity no greater than 0.2; heating the bis-Z-hydroxyethyl terephthalate at a temperature within the range of from about 230 C. to about 290 C., under a pressure of from 0.05 to 25 mm. of mercury, in the presence of a polymerization catalyst and at least 0.05% by weight, based on the weight of dimethyl terephthalate, of an organic phosphonate of the group hereinabove defined, until a film-forming polyethylene terephthalate (intrinsic viscosity of at least 0.45) is formed; extruding the molten polymer to form a self-supporting film; elongating the film at least 2.5X in at least one direpresentative sample of the above reaction residue gave the following results:

The material was undistillable. This analysis indicated a rection (where X is the original dimension of the film in compound of the following structure:

the direction of stretch), and heating the stretched film at a temperature of 150-250 C. to produce an oriented, heat-set film. Alternatively, the polymerization of the his- 2-hydroxyethyl terephthalate may be carried out directly by employing previously synthesized bis-2-hydroxyethyl terephthalate as a chemical intermediate in flake form.

The following specific examples will serve to further illustrate the principles and practice of this invention.

EXAMPLES 1-14 Samples of polyethylene terephthalate film were pre- OCII2CH3 OCHzCHa OCHQCH3 OCHzCHa within the temperaturerange betwen 230-290 C. under reduced pressure within the range from 0.052.5 mm. of mercury. During polymerization, glycol was continuously withdrawn from the reactor. The organic phosphonate dissolved in ethylene glycol (3% by Weight of phosphorus additive) was injected into the reactor after completion of the ester-interchange reaction. The polymerization reaction was carried out until a desired intrinsic viscosity was obtained, i.e., within the range of from 0.45 to 0.65. Thereafter, the polymer was introduced into an extrusion apparatus from which molten polymer was continuously extruded into film in amorphous form. The film was then cooled to room temperature on a quench roll.

The organic phosphonate compounds added to the polymerization reaction described were: (1) bis [2-bromoethyl (phenyl)] ethylene diphosphonate (2) hydroxypolyoxyethylene hydroxy methyl phosphonate, (3) the reaction product of triethyl phosphite and 2-chloroethanol, and (5) bis (2-chloroethyl) 1-[(2-chloroethyl) l- [(2-chloroethyl) 2-chloroethyl-phosphonate] ethylphosphonate] ethyl phosphonate.

The phosphonate compounds of (3) and (4) respectively, were prepared as follows:

Reaction between triethyl phosphite and 2-chloroethanol: Triethyl phosphite and 2-chloroethanol (one-toone mole ratio) were heated in a reaction vessel until the reaction mixture reached a temperature of approximately 200 C. Reaction by-products (ethanol and low boiling materials) were distilled off during the heating period. Preparation was completed by vacuum distillation of the reaction residue at temperatures up to 250 C. and a pressure of 15 mm. of mercury. Combustion analysis of a OOHzCHg OCHZCH3 OCHZCHB OCHQCHQ Samples of the above-prepared polyethylene terephthalate films along with polyethylene terephthalate film samples (control) prepared in a manner identical to those described hereinbefore, with the exception that the organic phosphonate component was not present or was replaced with the inorganic phosphorus compound, i.e-, monoammonium phosphate, were tested for film capacitor insulation resistance expressed as average resistivity in ohm/cm. 10 (single sheet test) and color expressed as percent yellow per five mil sample.

The insulation resistance was measured by the single sheet test dielectric method. In electrical applications in general, the insulating material or dielectric is subjected to electrical stresses which result in current flow in the dielectric. The current flow increases as a result of decreasing resistivity at elevated temperatures. In the case of capacitors, this effect is particularly important, as the flow of current results in higher temperatures and shorter life. The resistivity of polyethylene terephthalate film dielectric is measured by constructing a capacitor, using a film as a dielectric, and connecting a capacitor into a highresistant bridge circuit (General Radio Megohm Bridge Type 544-B). In the single sheet test dielectric method, a single sheet of test dielectric is used, and the resistance value measured in ohms is used to calculate volume resistivity (across opposite faces of the unit cube) in terms of ohm-centimeters. The single sheet measurement is made by painting a round electrode (one inch in diameter) on each side of the specimen of known thickness. The specimen is placed between brass plates of the electrode cell which is connected to the megohm bridge; the resistance in ohms at C. is used to calculate resistivity (r), in ohm-centimeters from the following relationship:

where r=the resistance in ohms at 125 C.; A=area in cm. t=thickness in centimeters.

Measurement of the color of the film samples was made on the color master and corrected to 5 mil thickness.

Table III lists for each example the phosphorus additive, weight percent of additive based on dimethyl terephthalate, the average resistivity in ohm/cm. 10 and the percent yellow based on a 5 mil thick sample.

TABLE IIL-EFFECT OF ORGANIC PHOSPHONATE DERIVATIVES ON ELECTRICAL RESISTANCE AND COLOR OF POLYETHYLENE TEREPHTHALATE FILMS Example Wt. percent Avg. resistivity Percent Average film Number Additive additive (based (ohm-cm. X yellow/ thickness on D T) mil (mils) 1 BZBMPPE 0.11 6. 08 2. 4. 5 2. B2BMPPE t). 17 9. 1. 83 4. 8 0. 23 11. 47 1. 87 4. 0 0. 17 20. 3O 2. 12 4. 6 t). 23 21. 1.87 5. 1 0.11 10. 1. 68 4. 1 0. 17 15. 50 1. 4. 5 0. 23 17. 1.21 3. 5 0.06 11. 10 1.99 4. 7 0. 11 19. 0. 94 5. 9

0. 17 25. 0. 82 t). 23 35. 10 1. 22 9. 1 0. 23 34. 47 1. 00 4. 6 0. 08 7. 70 3. 39 4. 1 0. 11 7. 40 7. 0 1. 40 3. Q5 4. 6 2. 2. 59 5. 0 3. 30 4. 81 4. 3 Do 0 2.70 5.16 4.7

B2BMPPE-2-Bromoethyl (phenyl) ethyl diphosphonate.

2 POEHMP-Hydroxy-polyoxyethylene hydroxymethyl phosphonate. PPB RReaction product of triethyl phosphite and Z-bromoethanol.

4 PPCL-Reaetion product of trieth phosphite and 2-chloroethan Y 01 BZCEPBis(2-chloroethyl)l-[(2-chloroethyl)1-[(ikehloroethyl)."l ehloroethyl phosphonate] ethyl phosphonate] ethyl phosphonate.

EXAMPLES 15-16 The percent yellow per 5 mil sample was measured by the color master." Table IV lists for each example the additive employed. weight percent of additive, average capacitor insulation resistance, and percent yellow per 5 mil sample. As a control example, polyethylene terephthalate film was prepared in the above-identified manner except that the organic phosphonate derivative was replaced by monoammonium phosphate.

TABLE IV.EFFECT OF ORGANIC PHOSPHONATE DERIVATIVES ON ELECTRICAL RESISTANCE AND COLOR OF POLYETHYLENE TEREPHTHALATE FILMS Avg. capacitor Example Wt percent insulation Percent Average film Number Additive additive (based resistance yellow/5 thickness on DMT) (megohms x mil (mils) microfarads) 0. 23 1, 239 1. 59 0. 7 POEHMP 0.23 458 2.01 0.8 Monoammonium phosphate. 0 09 830 8. 64 0. 7

l PPCL-Reaction product of triethyl phosphite and 2-chloroet-hanol. 2 POEHMP-Poly0xyethylene hydroxymethyl phosphonate.

of DMT), an organic phosphonate was added to the reaction mixture. PP-Cl (the reaction product of triethyl phosphite and 2-chloroethanol) and :hydroxy-polyoxyethylene hydroxymethyl phosphonate were the additives employed. After extrusion and quenching, the films were then continuously stretched longitudinally and then transversely to substantially the same extent (3X its initial dimension) in each direction to form a substantially balanced film, i.e., physical properties being substantially the same in both directions. Finally, the films were heat set at 200 C. while held under tension. The average capacitor insulation resistance and percent yellow/5 mil sample were measured for representative film samples. The average capacitor insulation resistance was measured by assembling a wound capacitor and evaluating a dielectric in terms of megohms vs. microfarads. The wound capacitor consists of alternate single layers of polyethylene terephthalate film (2 inches width) and of aluminum 1 /2 inches in width. The length of the film wound into the capacitors is determined by the desired capacitance. The resistance of the wound capacitor is measured at C. on a megohm bridge and then the capacitance is measured under the same conditions using a Cornell-Dubilier came gohms X microfarads value.

EXAMPLES 17-28 Samples of substantially amorphous polyethylene terephthalate film were prepared in a manner described in the previous examples. The catalyst system employed was identical with that employed hereinbefore. Prior to polymerization from ODS-0.34% (based upon the weight of DMT) of an organic phosphonate derivative was added to the reaction mixture. Hydroxy-polyoxyethylene chloromethyl phosphonate, hydroxy-polyoxyethylene trichloromethyl phosphonate and bis(2-bromoethyl) phosphonate were the additives employed. After extrusion and quenching, the films were then stretched in the machine direction (LD) to an extent of approximately 3X. The films were heat set at 200 C. while held under tension. The average resistivity in ohmsxcm. measured as described hereinbefore by the single sheet test dielectric method and the percent yellow per five mil sample was measured for these film samples. Table V lists for each example the additive employed, weight percent additive, average resistivity (ohmsxcm. 10 and percent yellow per 5 mil film sample. To serve as control example, a polyethylene terephthalate film sample was prepared identically described above with the exception that either monoammonium phosphate was substituted for the organic phosphonate, or no additive was employed.

TABLE V.EFFECT OF ORGANIC PHOSPHONATE DERIVATIVES ON ELECTRICAL RESISTANCE AND COLOR OF POLYETHYLENE TEREPHTHALATE FILMS Example Wt. percent Avg. resistiv- Percent yellow] Average film Number Additive additive (based ity (ohm-cm. mil thickness on DMT) X (mils) 17. POECMP 0. 08 56. 2 2. 78 2. 4 18. 0. 17 54. 9 2. 40 2. 2 19. 0. 26 38. 8 1. 67 2. 8 20. 0. 34 68. 1 1. 40 2. 2 21-.. 0. 08 60. 1 2. 28 2. 4 22 0. 17 54. 4 2. 07 2. 6 23..-- 0. 26 62. 6 1. 34 2. 3 24.- 0. 34 65. 8 1. 07 2. 2 25 Bis (2-bromoethyl) 2-bromo- 0. 08 41. 5 2. 23 2. 4

ethyl phosphonate. 0 0.17 49.8 1.90 2.5 .do 0. 26 52. 1 1.86 2.1 28.. ..-do 0.34 60.3 2.21 2.5 Control Monoammonium phosphate" 0. 09 63. 8 2. 8

1 Hydroxy-polyoxyethylene chloromethylphosphonate. Hydroxy-polyoxyethylene trichloromethyl phosphonate;

EXAMPLES 29-33 Samples of substantially amorphous polyethylene terephthalate were prepared as described hereinbefore. The catalyst system employed was identical with that employed in the previous examples. Dimethyl methyl phosphonate in amounts varying between 0.14 and 0.58% (weight percent based on weight of DMT) was added with the catalysts employed, either during ester interchange reaction between the DMT and ethylene glycol, or just prior to polymerization of the monomer after being reacted with ethylene glycol in the presence of a catalyst (e.g., lithium hydride). In both cases the dimethyl methyl phosphonate was converted to a glycol-phosphonate derivative. After polymerizing, the polymer was extruded in the form of a film 5 mils thick and quenched in a manner such as described hereinbefore. Representative samples of the film were tested for capacitor insulation resistance by the single sheet method as previously described. Table VI lists each example, the additive employed, method of addition, weight percent additive, and average resistivity.

TABLE VI.EFFECT OF ORGANIC PHOSPHONATE DERIVATIVES ON POLYETHYLENE TEREPHTHALATE FIL in both directions. The films were then heat-set at 200 C. while being held under tension. Representative samples of these films were tested for insulation resistance (in a manner described in Examples 15 and 16) and color. Color determinations were made using the trifiuoroacetic acid (TFA) method of determination. This determination was conducted as follows: 2-2.5 grams of polymer were placed in a spoflord flask to which was added distilled trifiuoroacetic acid. Ten mils of trifiuoroacetic acid were added per one gram of polymer. The flask Was put on a shaker and was shaken at room temperature until the polymer completely dissolved (approximately one hour). The color analysis was run on a Beckmann E-U spectrophotometer. For these determinations a 10 milliliter Pyrex cell was employed. The cell was first washed out with trifiuoroacetic acid. The absorbence of the polymer solution was run at an absorbence of 400 millimicrons and was compared to a blank cell filled with trifiuoroacetic acid. The color was reported as the absorbence. Table VII lists for each example the film (stretched) thickness,

1highCTRICAL RESISTANCE OF g V V r Wt. percent Avg. re- Average Example Additive How added additive sistivity film Number (based on (ohm-cm. thickness 29 Dimethyl methyl phosphonate--. Added during monomer prep 0. 14 11.77 4. 3 30.... do... Exchanged with ethylene glycol and 0.58 15.18 4. 7

added just prior to polymerization. 31-- d0.- o 0.58 14.00 7.5 32.. do Added during monomer prep 0. 14 12. 35 5.0 33.--- -d0 -d0 0.14 11.40 5.6 Control None 4. 97 3. 8 Do Monoammonium phosphate Added to monomer 0 09 10. 96 11. 2

EXAMPLES 3436 Samples of substantially amorphous polyethylene teradditive employed, weight percent of additive employed, insulation resistance (megohmsxmicrofarads), and color (TFA method).

TABLE VII.-EFFECT OF ORGANIC PHOSPHONATE DERIVATIVES ON ELECTRICAL RESISTANCE AND COLOR OF POLYETHYLENE TEREPHTHALATE FILMS Film Wt. percent Insulation Example thickness Additive employed additive resistance Color Number (stretched) (based on (megohms x TFA (mils) DMT) microiarads) 0.5 POEHMP 1 0.23 557 0. 117 0. 5 0. 23 590 0. 103 1. 0 0. 23 0. 000 0. 5 0. 09 429 0. 167

i POEEMF-Hydroxy-polyoxyethylene hydroxymethyl phosphonate. 2 PP-CL-Reaction product of triethyl phosphite and 2-chloroethanol.

EXAMPLES 37-39 Samples of substantially amorphous polyethylene terephthalate film were prepared by the direct polymerization of bis(beta-hydroxyethyl)terephthalate. The procedure was as follows: bis(beta-hydroxyethyl)terephthalate (DHET), the preparation of which is well known to the art, in the form of flake, was melted in a reaction vessel at C. Tetraisopropyl titanate in the concentration of one to two parts per million titanium based on the weight .of reactants was employed as the catalyst and was added in both the LD and TD to an extent of approximately 3X 7 directly to the DHET reaction vessel. Also added directly to the reaction ingredients was 0.146% hydroxy-polyoxyand feed nozzles being plugged by precipitated reaction ethylene hydroxymethyl phosphonate. The weight percent products. of the organic phosphonate was based on the weight of EXAMPLE 40 dimethyl terephthalate as the starting monomer. The reaction mass was heated to 140 C. to melt the monomer and catalyst. Excess ethylene glycol was distilled off by heating the reaction mixture to 230 C. for a period of 40 minutes. Polymerization of DHET to polyethylene terephthalate was then accomplished by heating the mixture by placing the reaction vessel in vapors of boiling dimethyl phthalate at a temperature of 282 C. and a pressure of 0.5-0.1 mm. of mercury for a period of two hours. The thus formed molten polymer was extruded in the form of a film and quenched on a quench roll maintained at a temperature of 7080 C. Samples of the extruded and 15 quenched film were stretched 3X in both the LD and TD and heat-set at 200 C. while being held under tension.

Tests were run on these test films for capacitor insula- Monomeric ethylene naphthalene 2,6 dicarboxylate was prepared by carrying out an ester-interchange reaction in a conventional manner between ethylene glycol and dimethyl naphthalene 2,6 dicarboxylate utilizing a catalyst system comprising manganous acetate and antimony trioxide (Sb O Three separate polymers were prepared from the abovedescribed monomer. All contained the same catalyst, but the first (Example 40) contained an organic phosphonate, the second an inorganic phosphate (ammonium dihydrogen phosphate), and the third had no additional additive. The formulations were as follows:

tion resistance, utilizing the single sheet method, and color, Example 1 G. utilizing the TFA test. As control examples, DHET was Ethylene naphthalene dicarboxylate polymerized in the same manner as described above with Omer 600 the exception that either monoammonium phosphate was Hydroxy polyoxyethylene hydroxymethyl substituted for the organic phosphonate derivative or no PhO Ph IIatB 0.88 phosphorus derivative was employed. In the case wherein Zin a tate dihydrate 0.07 monoammonium phosphate was employed, a catalyst sys- Antim nY trioxide 0.028 tem comprising 0.03% antimony trioxide (percent cata- Lithium hydride 0.019 lyst being based on the weight of DMT). Table VIII lists Control A: for each example the thickness of both the cast and y n napht alene 2,6 dicarboxylate monstretched film, catalyst system employed, phosphorus de- Omer 600 rivative employed, average resistivity f oni m dihydrogen phosphate 0.83 h m 1012) Zinc acetate dihydrate 0.07 m 0 ms c Antimony trioxide 0,028 and the color as measured by the TFA test. Lithium hydride 0.019

TABLE VIIL-EFFECT OF ORGANIC PHOSPHONATE DERIVATIVES ON ELECTRICAL RESISTANCE AND COLOR OF POLYETHYLENE TEREPHIHALATE FILMS Wt. percent Avg.

Thickness Thickness additive resistivity Example mils m Catalyst system Additive employed (based on (ohm-cm. 10) Color Number (cast) (stretched) (Based on percent DMT) DM'I as stretched (TFA) starting film monomer) 12.0 1.35 Tetraisopropyl titanate Hydrcxypolyoxyethylene 0.146 81 .052

phosphonate. 12.0 1.23 ..do ..do 0.146 97 .062 12.5 1. d0- .do- 0.146 80 .070 10.0 1.30 SbzOa Monoammonium phosphate 0.09 76 .167

As can be seen from the data set forth in the foregoing Control B: examples, the inclusion of the organic phosphonate de- Ethylene naphthalene 2,6 dicarboxylate monrivatives, as an additive in the step of polymerizing bis omer 600 (beta-hydroxyethyl)terephthalate to polyethylene tereph Zinc acetate dihydrate 0.07 thalate, in accordance with the present invention, results Antimony trioxide 0.028 in the following advantages: Lithium hydride 0.019

(1) Less inhibiting action on monomer polymerizadon-Because the organic phosphonates do not signifi- The polymerization reactions were carried out at a cantly deactivate the catalyst normally employed in the temperature of 285290 C. under reduced pressure withpolymerization system, economically feasible rates of in the range from 0.05-2.5 mm. of mercury. The polympolymerization are now possible and the full spectrum of erization reaction was carried out until the desired incatalysts available for the polymerization of polyethylene trinsic viscosity was obtained. It was observed that polterephthalate may be employed without the danger of sigymer containing the phosphonate (polymeric) had less nificant deactivation. color after polymerization than the other two polymers. (2) Significant improvement in polymer color.One Thereafter, the polymers were extruded into the form of major cause of film rejects by the consumer has been the a film and quenched. The films were then molecularly yellowness of films (due at least in part to the phosphorus oriented by stretching in a manner described hereinbefore additives employed). The use of the subject organic phosto an extent of 4X in both the longitudinal and transverse phonate derivatives in polyethylene terephthalate polymdirections. The films were heat-set at a temperature of erization system will materially reduce the yellowness of 220240 C. finished films and henceforth result in a significant eCo- The hydrolytic stability of the films prepared from the nomic gain. three polymer batches was tested as follows. A series of (3) Higher film capacitor insulation resistance.This small beakers filled with water were placed on the bottom improvement in insulation resistance will enable capaciof one gallon rectangular cans from which the tops had tors utilizing polyethylene terephthalate film as dielectric been removed. Samples of the films prepared from the to operate for longer durations without breakdown, parthree polymeric formulations described above were susticularly at elevated temperatures. pended in the can above the beakers of water. Aluminum (4) Less precipitation from reaction with other procfoil was placed over the can and the can was placed in ess catalysts and additives-The absence of reaction with an oven at 80 C. Periodically the film samples were reother catalytic agents results in less time lost due to opmoved and tested for brittleness by manually flexing the eration shutdowns heretofore required because of filters film in a rapid manner. After flexing, the film samples were scrutinized for evidence of cracking. These hydrobis 2 hydroxyethyl terephthalate and the his 2 hylytic stability tests showed that films from Example 40 droxyethyl terephthalate is subsequently polymerized to (containing the organophosphonate) were still flexible form film-forming polyethylene terephthalate in the after 345 days in the 100% RH. atmosphere at 80 C. presence of a catalyst effective to promote polymeriza- Control A (containing the inorganic phosphate) failed tion, the improvement which comprises polymerizing after 75 days. The polymeric film to which no phosphosaid bis-2-hydroxyethyl terephthalate in the presence of rous additive had been added (Control B) failed after from 0.05% to 1% by weight of an organic phosphonate 110 days. When samples of the oriented film from the selected from the group consisting of the organic phosthree polymer compositions were subjected in an oven phonate resulting from the reaction between triethyl phosat a temperature of 200 C. for a prolonged period, it phite and 2-chloroethanol and having the formula was found that the Control B films failed due to oxidative the organic phosphonate resulting from the reaction bedegradation after 137 hours, the Control A films failed tween triethyl phosphite and 2-bromoethanol and having after 145 hours, and those of the example failed after the formula 300 hours. Thus, greater than two-fold improvement was and the organic phosphonate resulting from the ester-inter- IealiZed for the film P p aeeordylg t0 lnventlollchange reaction between dimethyl methylphosphonate Similar improvements in hydrolytrc stability were ob and ethylene glycoL served for films of polyethylene terephthalate prepared f g the orgamc phosphonate catalyst 2 The process 0 claim 1 wherein the organlc phos phonate is the organic phosphonate resulting from the EXAMPLE 41 reaction between triethyl phosphite and 2-chloroethanol Two separate ester-interchange reactions were carried and having the formula out in a conventional manner between ethylene glycol and 3. The process of claim 1 wherein the organic phosa mixture of dimethyl bibenzoate and dimethyl 4,4'-isophosphonate is the organic phosphonate resulting from propylidene dibenzoate. In one case, an organic phosphothe reaction between triethyl phosphite and 2-bromonate (hydroxy-polyoxyethylene hydroxymethyl phosphoethanol and having the formula nate) was included in the reaction and in the other, the 4. The process of claim 1 wherein the organic phoscontrol, no phosphonate was added. The formulations for phonate is the organic phosphonate resulting from the the preparation of monomer were as follows: 5 ester interchange reaction between dimethyl methylphosphonate and ethylene glycol. Example 41: G.

Dimethyl bibenzoate 432 References Cited gtilrlneilrilyl ifggilsopropylidene bibenzoate UNITED STATES PATENTS MHiOAZi-ZH 6"::::::::::::::::: 6.1962 2,871,204 3/1959 Duhnkmck et sbzos f jjjj j 0,1164 3,052,653 9/1962 Iannicelli 260-75 Hydroxy polyoxyethylene hydroxymethyl 3,058,935 10/1962 Starck et al. 26075 phosphonate (added in 1.5 ml. ethylene 9,450 6/1964 Fnedman 26o 75 glycol) 0 17 7, 6/19 6 Schoepfle 01; a1. 260-75 control! b 1 b b (1 6 1 432 FOREIGN PATENTS Dime Y i enzoate es) 1 377 064 9/1964 France Dimethyl 4,4 -1sopropyl1dene blbenzoate (0.4 124 883,754 12/1961 Great Britain m0 6) 601,309 7/1960 Canada. Ethylene glycol moles) 273 601 310 7 19 0 Canada. Mn(OA)2'4H20 0-1962 568,816 12/1958 Belgium. sbzos 0-1164 1,016,511 1/1966 Great Britain.

1,341,506 9/1963 France.

After the ester-mterchange react1on was complete, the two monomers were polymerized by conventional meth- 5 OTHER REFERENCES The Polymer Obtained from the Control (P P Gefter: Organophorus Monomers and Polymers, pp. nate free) was strongly colored. The polymer of Exarn- IX-XV, published 1962 by Associated Technical Serple 41 (phosphonate containing) was very lightly colored. vices Inc., Glen Ridge, N.J., QD 412-P1 G4.

We claim: Kosolapoff: Organophosphorus Compounds, p. 4,

1. In the process of producing polyethylene tereph- John Wiley & Sons, Inc., N.Y., 1950, QD412PIKS. thalate wherein dimethyl terephthalate is reacted with ethylene glycol in the presence of an ester interchange WILLIAM H'SHORTPrlmary Exammer' catalyst to effect ester interchange with the formation of LOUISE P. QUAST,Assistant Examiner. 

